Solid-state imaging workstations, that are configured either as vertical slot scanners each having a generally vertically arranged, upright window, or as flat-bed or horizontal slot scanners each having a generally horizontally arranged window, or as bi-optical, dual window scanners each having both generally horizontally and vertically arranged windows, or as stand-mounted, stationary scanners each having a presentation window, have been installed in many venues, such as supermarkets, department stores, and other kinds of retailers, as well as warehouses, and other kinds of industrial settings, for many years, to electro-optically read by image capture a plurality of symbol targets, such as one-dimensional symbols, particularly Universal Product Code (UPC) bar code symbols, and two-dimensional symbols, as well as non-symbol targets, such as driver's licenses, receipts, signatures, etc., the targets being associated with, or borne by, objects or products to be processed by the workstations. An operator or a customer may slide or swipe a product associated with, or bearing, a target in a moving direction across and past a respective window of the workstation in a swipe mode. Alternatively, the operator or the customer may momentarily present the target associated with, or borne by, the product to an approximate central region of the respective window, and steadily momentarily hold the target in front of the respective window, in a presentation mode. The choice depends on user preference, or on the layout of the workstation, or on the type of the target.
The symbol target may be located low or high, or right to left, on the product, or anywhere in between, on any of six sides of the product. The symbol target may be oriented in a “fence” orientation in which elongated parallel bars of the UPC symbol are vertical, or in a “ladder” orientation in which the UPC symbol bars are horizontal, or at any tilted orientation angle in between the fence and ladder orientations. The products may be held by the user at various tilt angles during their movement across, or presentation to, either window of the bi-optical workstation. The products may be positioned either in contact with, or held at a distance away from, either window during such movement or presentation. All these factors make the symbol location variable and difficult to predict in advance.
Known imaging workstations typically include multiple, solid-state imagers, each comprising an array of pixels or sensors arranged along mutually perpendicular array axes, for sensing return light returning through at least one window of the workstation from a target being imaged. Each imager may be a two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device, operable at a frame rate, and is analogous to the image sensors used in electronic digital cameras. The known imaging workstations also typically include an illuminating light system for illuminating the target with illumination light from an illumination light source, e.g., one or more light emitting diodes (LEDs), through each window of the workstation; an imaging lens assembly, e.g., one or more imaging lenses, for capturing return ambient and/or illumination light scattered and/or reflected from the target through each window of the workstation over a main field of view and over a range of working distances relative to each window; and electrical circuitry for producing electronic analog signals corresponding to the intensity of the light captured by the image sensor over the main field of view, and for digitizing the analog signal. The electrical circuitry typically includes a controller or programmed microprocessor for controlling operation of the electrical components supported by the workstations, and for processing each target and/or decoding the digitized signal based upon a specific symbology when the target is a symbol.
To enable reliable reading of targets that could be positioned anywhere on all six sides of a three-dimensional product, some known imaging bi-optical workstations require about ten to twelve, or at least six, of such imagers in order to provide a full coverage scan zone that extends above the horizontal window and in front of the upright window so that the scan zone extends down as close as possible to the countertop, and sufficiently high above the countertop, and as wide as possible across the width of the countertop. The scan zone projects into space away from the windows and grows in volume rapidly in order to cover targets on products that are positioned not only on the windows, but also many inches therefrom. The scan zone must be large enough to read targets positioned in any possible way across the entire volume of the scan zone and must not have any dead areas in which targets are not covered and, therefore, cannot be read.
To bring the cost of the known imaging workstations down to an acceptable level, it is known to reduce the need for so many imagers down, for example, to two imagers, or even one imager, by splitting the main field of view of at least one of the imagers into a plurality of subfields of view, each additional subfield serving to replace an additional imager. The subfields diverge as they pass through the windows, thereby reducing resolution when imaging targets that are approximately parallel to the windows (a common situation), because the projection of individual sensors on the targets is also enlarged. If a target is being imaged by an outer subfield angled to the right or left of the workstation, then the projection of the sensors on the target is stretched to the right or left. If the target is being imaged through one window by a central subfield directed towards the opposite window, then the sensor projection is stretched at right angles to the stretch from the outer subfields. In other words, for each window, there are subfields that have a higher resolution along a horizontal (left/right or right/left) axis, and different subfields have a higher resolution along a vertical (up/down or down/up) axis.
Anamorphic optics have been proposed for use in the imaging lens assembly of each imager to change the size of the main field of view of each imager not only to fit the main field of view through each window, but also to optimize the resolution of each main field of view along both of the two mutually perpendicular array axes, thereby enabling reading of a symbol target in a single main field of view, no matter whether the symbol target is in the ladder orientation, or the fence orientation, or in another tilted orientation inclined between the ladder and fence orientations. In other words, each main field of view was optically configured and optimized along two mutually perpendicular directions to read the symbol target regardless of target orientation.
Anamorphic optics, however, require optical alignment and increase the cost of the workstation and decrease manufacturing efficiency. Even so, anamorphic optics are not readily usable in workstations where the main field of view is split into subfields, because the anamorphic optics would optically modify all the subfields from a single imager in the same way, and there would be no individual control over changing the size and resolution of each subfield. In other words, one of the subfields might be optimized to read the symbol target regardless of target orientation along one direction, but the other subfields would not be so optimized, and, as a result, the scan zone would have the aforementioned dead areas.
Accordingly, there is a need for an apparatus for, and a method of, reading targets in an imaging workstation where the main field of view is split into subfields to reduce the number of imagers required, and to reliably read such targets despite being arbitrarily oriented in the imaging workstation, without using anamorphic optics.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.